I have a persistent, but infrequent situation where a message from a mail list will appear in the list of messages twice. The IDs are identical between the copies. There is only one copy of the email in the mailbox. It appears that there are two entries in some index. Apple's mail gets confused by this. If I delete the first entry, the second remains but is tagged as found in mailbox NULL. It cannot easily be deleted.
My first thought was that sieve was saving two copies. So I pulled a copy of the original email and ran sieve-test on it. It is only saved once to the proper mailbox. I have not been able to determine if the problem is in Dovecot or Apple's mail app. From what I see, it could be either. I would appreciate any ideas on how to diagnose this further. Thanks,
-- Doug